Glossary
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TermDefinition
- Abbreviation, Light Characteristic Occulting (Oc)
A light with more light than dark (is on for longer than it is off).
Occulting refers to a type of navigational light in which the light is...
More Details - General Nautical Terminology Ocean Data Acquisition System (ODAS)
The Ocean Data Acquisition System (ODAS) is a system used to collect, process, and transmit various types of oceanographic data. This system...
More Details - Flag / Pennant, Signals & Communication Code Flag Oscar (O)

The International Maritime Signal Flag Oscar.
Meaning
Man overboard. (Often attached to the Danbuoy pole on boats.)
The semaphore flag. - General Nautical Terminology ODAS
The Ocean Data Acquisition System (ODAS) is a system used to collect, process, and transmit various types of oceanographic data. This system...
More Details - General Nautical Terminology Officer of the Watch (OOW)
The designated officer responsible for the safe navigation and operation of a vessel during their assigned watch period.
The Officer of the...
More Details - General Nautical Terminology Offshore
The area of the sea that is away from the coast, typically beyond the immediate inshore waters, and often associated with deeper waters and...
More Details - Courses, RYA Offshore Personal Survival (RYA/World Sailing)The Offshore Personal Survival course is an intensive program designed for sailors participating in offshore and ocean races. Participants learn... More Details
- General Nautical Terminology OilskinsWaterproof clothing worn in foul weather
- Flag Semaphore, Signals & Communication Letter O (Flag Semaphore)

Flag semaphore indicating the letter O.
- Morse Code, Signals & Communication Letter O (Morse Code)
International Morse Code sequence representing the letter O.
- General Nautical Terminology OnshoreWind blowing towards the land or “not at sea”.
- General Nautical Terminology, Parts of a Boat On the Port Bow
Refers to something located in the forward left quadrant of a vessel, between directly ahead and 90 degrees to the port (left) side.
"On the...
More Details - General Nautical Terminology On the Port QuarterAt an angle to the stern of your vessel, but abaft the beam, to the left
- General Nautical Terminology, Parts of a Boat On the Starboard Bow
Refers to a position or object located forward of the vessel and to the right-hand side when facing the bow (front) of the ship.
"On the...
More Details - General Nautical Terminology, Parts of a Boat On the Starboard Quarter
The area of a vessel located towards the rear (aft) on the right-hand side when facing forward.
The phrase "on the starboard quarter" is a...
More Details - General Nautical Terminology OOW
The designated officer responsible for the safe navigation and operation of a vessel during their assigned watch period.
The Officer of the...
More Details - Phonetic Alphabet, Signals & Communication Oscar
Pronounced: OSS-cah
The term for the letter O in the NATO Phonetic Alphabet.
- General Nautical Terminology, Parts of a Boat Outhaul
A line or tackle system used to adjust the tension and position of the sail's clew along the boom, affecting the sail's shape and...
More Details - General Nautical Terminology OverfallsTurbulent waters where is a sudden change in depth or where two tidal streams meet
- General Nautical Terminology Overhand loop
A loop that crosses on top of the standing part of a rope when tying a knot.
- General Nautical Terminology PainterThe line at the bow of a dinghy
- General Nautical Terminology, Safety, Signals & Communication Pan Pan
An internationally recognised maritime urgency signal used in radio communications to indicate a situation that is urgent but does not pose an...
More Details - Phonetic Alphabet, Signals & Communication Papa
Pronounced: pah-pah
The term for the letter P in the NATO Phonetic Alphabet.
- General Nautical Terminology, Safety Parachute Flare
A pyrotechnic distress signal that, when launched, ascends to a high altitude before deploying a parachute to slow its descent while emitting a...
More Details - General Nautical Terminology Parallel RulesNavigational instrument used in conjunction with the compass rose on the chart to transfer bearings and courses to plot a vessel’s position
- General Nautical Terminology, Navigation, Safety Passage
A journey or route taken by a vessel from one location to another, often across open water or between specific points such as harbours or...
More Details - General Nautical Terminology, Navigation, Safety Passage Plan
A detailed, structured navigational strategy outlining the safest and most efficient route for a vessel from departure to destination,...
More Details - General Nautical Terminology Pay Off
The action or process of a vessel's bow turning away from the wind, often due to wind or rudder adjustments.
When a vessel "pays off," it is...
More Details - General Nautical Terminology Pay OutTo let out a line or rope gradually
- Flag / Pennant, Signals & Communication Code Flag Papa (P)

The International Maritime Signal Flag Papa.
Meaning
The Blue Peter.
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In harbour: All persons should report on board as the vessel is... - General Nautical Terminology, Navigation PDOP
Measurement of the geometric strength of satellite configuration in a Global Navigation Satellite System (GNSS) receiver.
It quantifies the...
More Details - General Nautical Terminology Perling
The small, gentle ripples or wavelets that form on the surface of the water, typically caused by light winds or minor disturbances.
Perling...
More Details - General Nautical Terminology, Safety Personal Flotation Device (PFD)
A piece of equipment designed to assist a person in staying afloat in water by providing buoyancy.A Personal Flotation Device (PFD), commonly...
More Details - General Nautical Terminology, Safety Personal Locator Beacon (PLB)
A compact, portable device used to transmit a distress signal via satellite to alert search and rescue services in emergencies at sea.

A...
More Details - Courses, RYA Personal Watercraft ProficiencyThe RYA Personal Watercraft Proficiency course is designed for jet ski operators, covering essential skills for safe and enjoyable use.... More Details
- General Nautical Terminology, Safety PFD
A piece of equipment designed to assist a person in staying afloat in water by providing buoyancy.A Personal Flotation Device (PFD), commonly...
More Details - Phonetic Alphabet, Signals & Communication Phonetic Alphabet
The Phonetic Alphabet, also known as the International Radiotelephony Spelling Alphabet or NATO phonetic alphabet, is a standardised set of words...
More Details - General Nautical Terminology PileA stout timber or metal post driven vertically into the a river or seabed
- General Nautical Terminology PilotAn expert in local waters who assists vessels entering or leaving harbour; An official publication posting details of, for example, local coasts,... More Details
- General Nautical Terminology, Navigation Pilotage
Pilotage is the use of fixed visual references by sight or radar to safely navigate to a destination, usually a port or harbour, with the help of...
More Details - General Nautical Terminology PinchTo sail too close to the wind so that the sails lose driving power
- Did you know?, Nautical Saying Pipe down
Pipe down is a nautical term meaning to quiet down or cease talking. It is often used as a command on a boat or ship to instruct crew members or...
More Details - General Nautical Terminology Pitch
The angle or inclination of a vessel's bow and stern as it moves up and down in response to waves.
Pitch is a critical concept in marine...
More Details - General Nautical Terminology Pitch Pole
A capsize where a boat flips longitudinally, usually caused by the bow digging into a wave or sudden deceleration.
A pitch pole is a dramatic...
More Details - General Nautical Terminology, Safety PLB
A compact, portable device used to transmit a distress signal via satellite to alert search and rescue services in emergencies at sea.

A...
More Details - Flag Semaphore, Signals & Communication Letter P (Flag Semaphore)

Flag semaphore indicating the letter P.
- Morse Code, Signals & Communication Letter P (Morse Code)
International Morse Code sequence representing the letter P.
- General Nautical Terminology PlotTo find a vessels position by laying off bearings on a chart
- General Nautical Terminology, Weather (Meteorology) Plymouth
Sea area of the Met Office Shipping Forecast. Spans Plymouth Sound and adjacent waters off southwest England.
From Plymouth Sound (“mouth of the...
More Details - General Nautical Terminology Pontoon
A pontoon is a flat, buoyant structure used to support a platform, bridge, or boat. It is typically made of metal, plastic, or inflatable...
More Details - General Nautical Terminology PoopedSwamped by a high, following sea.
- General Nautical Terminology, Parts of a Boat Port
The left-hand side of a vessel when facing forward towards the bow.
The term "port" is used in maritime navigation to refer to the left side...
More Details - General Nautical Terminology Port
A Harbour or docking facility where vessels load and unload cargo or passengers.
A port is a designated location along a coast, river, or...
More Details - General Nautical Terminology, Parts of a Boat Port Beam
The side of a vessel that is perpendicular to its centreline and located on the left-hand side when facing forward towards the bow.
The term...
More Details - General Nautical Terminology, Parts of a Boat Port Bow
The forward left-hand side of a vessel when facing the bow (front).
The term "port bow" is a specific designation used in nautical contexts to...
More Details - General Nautical Terminology PortholeAn aperture on the hull of a vessel that admits light and, sometimes, air
- General Nautical Terminology, Weather (Meteorology) Portland
Sea area of the Met Office Shipping Forecast. Located off the south coast of England, near Portland Bill in Dorset.
Named for Portland Bill on...
More Details - General Nautical Terminology, Navigation Portland Plotter
A navigational tool used in marine chartwork to measure and plot courses, bearings, and distances on nautical charts.

The Portland Plotter...
More Details - General Nautical Terminology Port of RegistryThe port listed in a vessel’s registration documents and lettered on her stern
- General Nautical Terminology, Parts of a Boat Port Quarter
The aft-left section of a vessel when facing forward, located between the port beam and the stern.
The term "port quarter" is a specific...
More Details - General Nautical Terminology Port Tack
The situation in sailing where the wind is coming over the port (left) side of the vessel, and the boom is positioned on the starboard (right)...
More Details - General Nautical Terminology, Navigation Position Dilution of Precision (PDOP)
Measurement of the geometric strength of satellite configuration in a Global Navigation Satellite System (GNSS) receiver.
It quantifies the...
More Details - Courses, RYA Powerboat AdvancedThe RYA Powerboat Advanced course is designed for experienced powerboaters operating in challenging conditions, including night navigation.... More Details
- Courses, RYA Powerboat IntermediateThe RYA Powerboat Intermediate course bridges the gap between Level 2 and advanced powerboating. Participants learn navigation, passage planning,... More Details
- General Nautical Terminology Pratique
The official permission granted to a vessel by port health authorities, allowing it to enter a port and conduct operations after confirming it is...
More Details - General Nautical Terminology, Weather (Meteorology) Precipitation
Any form of water, such as rain, snow, sleet, or hail, that falls from the atmosphere and reaches the Earth's surface.
Precipitation is a key...
More Details - Did you know?, Nautical Saying Pressed into service
Pressed into service is the term used to describe the action of the British Navy filling their ships’ crew quotas by kidnapping men off the...
More Details - Did you know?, Nautical Saying Press Gangs
Press gangs were groups of men employed by the British Royal Navy in the 17th to 19th centuries to forcibly recruit individuals into naval...
More Details - General Nautical Terminology Prevailing WindThe wind direction that occurs most frequently at a place over a certain period
- General Nautical Terminology Preventer
A line or tackle rigged to the boom or spar to prevent unwanted movement, particularly to stop a boom from swinging dangerously during an...
More Details - General Nautical Terminology, Navigation Prime Meridian
The zero-degree longitude line that is the starting point for measuring longitude and dividing the Earth into the Eastern and Western...
More Details - General Nautical Terminology, Signals & Communication Procedure Words
Standardised words or phrases used in marine radio communication to ensure clarity, reduce misunderstandings, and maintain efficient and safe...
More Details - Courses, RYA Professional Practices and ResponsibilitiesThe RYA Professional Practices and Responsibilities (PPR) course is a mandatory online qualification for individuals seeking a Commercial... More Details
- General Nautical Terminology Propeller
A propeller is a fan-like device that propels a boat or ship through the water by converting rotational motion into thrust. Propellers typically...
More Details - General Nautical Terminology Propeller Shaft
A propeller shaft is a long, cylindrical metal shaft that connects the boat's transmission or gearbox to the propeller. It transmits power from...
More Details - General Nautical Terminology Propeller Walk
The lateral movement of a boat's stern caused by the rotational forces of the propeller, typically noticeable when operating at low speeds or in...
More Details - General Nautical Terminology Propeller Wash
The turbulent flow of water generated by a vessel's propeller as it moves through the water, often creating strong currents and turbulence behind...
More Details - General Nautical Terminology Pulpit
A raised structure at the bow of a vessel, often made of metal, designed to provide safety for crew members working at the front of the...
More Details - General Nautical Terminology Pushpit
A sturdy, protective railing or guardrail located at the stern of a boat, often forming part of the vessel's safety framework.
The pushpit,...
More Details - General Nautical Terminology, Safety Pyrotechnic
A device or material designed to produce light, heat, smoke, or sound through a chemical reaction, commonly used in marine signalling for...
More Details - Flag / Pennant, Signals & Communication Code Flag Quebec (Q)

The International Maritime Signal Flag Quebec.
Meaning
Quarantine Flag.
My vessel is healthy and I request free pratique. - General Nautical Terminology Q FlagYellow flag flown from starboard spreaders or flagstaff when entering a foreign port (or Channel Isles) requesting customs clearance. Don’t remove... More Details
- Flag Semaphore, Signals & Communication Letter Q (Flag Semaphore)

Flag semaphore indicating the letter Q.
- Morse Code, Signals & Communication Letter Q (Morse Code)
International Morse Code sequence representing the letter Q.
- General Nautical Terminology Quarter Berth
A small sleeping area located beneath the cockpit on a sailing or motor vessel, typically positioned on one side of the boat's stern.
A...
More Details - Phonetic Alphabet, Signals & Communication Quebec
Pronounced: keh-BECK
The term for the letter Q in the NATO Phonetic Alphabet.
- General Nautical Terminology RaceA strong tidal stream
- Courses RadarThe RYA Radar course teaches participants to use radar systems effectively for navigation and collision avoidance. Topics include radar setup,... More Details
- General Nautical Terminology, Safety Radar Reflector
A passive device designed to enhance a vessel's visibility on radar systems by reflecting radar signals back to their source.
A radar...
More Details - General Nautical Terminology, Safety Radio Medical Advice Link Call (MEDILINK)
A communication made via radio from a vessel to a shore-based medical facility or professional to seek urgent medical advice or assistance for an...
More Details - General Nautical Terminology RaftTwo or more vessels tied up alongside each other
- Abbreviation, General Nautical Terminology RAM
A ship that, due to the nature of its work, is unable to keep out of the way of other vessels as required by the International Regulations for...
More Details - General Nautical Terminology, Navigation Range of Tide
The vertical difference between the high tide and the succeeding low tide in a specific tidal cycle.
The range of tide is a fundamental...
More Details - General Nautical Terminology Raster chartElectronic chart which is a direct copy of a paper chart with limited zooming capability
- General Nautical Terminology, Navigation Rate (Tidal Stream)
The speed at which a tidal stream flows, typically measured in knots.
The rate of a tidal stream is the velocity at which the water moves due...
More Details - Flag / Pennant, Signals & Communication Code Flag Romeo (R)

The International Maritime Signal Flag Romeo.
Meaning
Distance (range) in nautical miles. Given using Numeral Pennants.
- General Nautical Terminology Reach
The point of sail where the wind is coming from the side of the boat, roughly perpendicular to the direction the boat is travelling.
A reach...
More Details - General Nautical Terminology ReachingSailing across the wind: from about 60° to about 160° off the wind. Reaching consists of "close reaching" (about 60° to 80°), "beam reaching"... More Details
- General Nautical Terminology Ready AboutThe helmsman’s shout that he intends to go about shortly
- Flag Semaphore Ready (Flag Semaphore)

The Ready (Flag Semaphore) signal shows the sender is ready to send a message. The same shape is also used for Space (Flag Semaphore) & Rest...
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